Various methods for operating transmission systems, and controlling shifting of transmissions in vehicles, have been implemented to increase the gas mileage of the vehicle.
In one approach, U.S. Pat. No. 6,813,550, the shifting of the transmission can be adjusted based on a prediction of fuel economy before and after the shift. For example, the predictive system allows the transmission to up-shift when the fuel economy predicted after the shift is decreased. The up-shift is carried out automatically, regardless of the intention of the driver. A fuel consumption ratio map is used to predict what effect the up-shift will have on fuel economy. The ratio map stipulates the relationship between fuel economy, engine speed, and engine torque.
However, the inventors herein have recognized various issues with the above approach. Specifically, due to the varied ambient conditions experienced by the vehicle, the system may incorrectly predict that the up-shift will increase fuel economy. In particular, for a given speed and torque under some ambient conditions, such as cold temperatures and/or high humidity ambient conditions, the system may predict, correctly, that the up-shift will increase fuel economy. However, for the same speed and torque condition, but under different ambient conditions, such has hot temperatures and/or low humidity ambient conditions, the system may predict, incorrectly, that the up-shift will increase fuel economy. Under these latter conditions, spark knock may occur, thus resulting in a retarded ignition timing—where the retarded ignition timing causes the fuel economy to actually decrease after the up-shift.
Thus, in one approach, a method for operating an engine and transmission in a vehicle is provided. The method comprises up-shifting the transmission based on whether engine knock limits spark advance at engine conditions after the up-shift. For example, the decision as to whether to execute an up-shift at the current conditions may take into account ambient effects on engine knock, and the corresponding ignition timing retard, in identifying whether fuel flow will actually decrease in the up-shifted gear.